The kinetics of phase transformation of nanocrystalline anatase samples was studied using x-ray diffraction at temperatures ranging from 600 to 1150 °C. Kinetic data were analyzed with an interface nucleation model and a newly proposed kinetic model for combined interface and surface nucleation. Results revealed that the activation energy of nucleation is size dependent. In anatase samples with denser particle packing, rutile nucleates primarily at interfaces between contacting anatase particles. In anatase samples with less dense particle packing, rutile nucleates at both interfaces and free surfaces of anatase particles. The predominant nucleation mode may change from interface nucleation at low temperatures to surface nucleation at intermediate temperatures and to bulk nucleation at very high temperatures. Alumina particles dispersed among the anatase particles can effectively reduce the probability of interface nucleation at all temperatures.

The aim of this study is to demonstrate that the electronic and structural properties of II–VI substrates, here ZnTe, can be dramatically affected by thermal heating at temperatures in the range of those typically used in the epitaxial metalorganic chemical vapor deposition processes. Photoluminescence response shows that annealing at these temperatures produces a reduction of the sample crystalline quality, decreasing the free exciton emission relative to the deep level related one. Some factors, like the change in the charge and stress state of dislocations, Cu diffusion, and oxygen incorporation, could be responsible for changes in the substrate properties, which can produce stresses and contamination in the deposited sample.

The structural and electronic properties of (CdTe)1−x(In2Te3)x thin films as a function of substrate temperature were studied using x-ray diffraction, energy dispersive x-ray analysis, and Raman, transmission, and modulated transmission spectroscopies. The films were grown by the close-spaced vapor transport technique combined with free evaporation; CdTe and In2Te3 were used as sources. From x-ray diffraction the presence of mixed phases and differences in composition were detected, and good correlation with Raman spectroscopy was found. Transmission spectroscopy suggested the possibility of a modulation of the band gap of the alloy from a value as low as 0.5 eV up to 1.5 eV. Single-phase films presented a direct band gap of around 1.15 eV, as obtained from modulated transmission measurements.

A diffuse phase transition for Pb(Zn1/3Nb2/3)O3–PbZrO3–PbTiO3 (PZN-PZ-PT) system in the rhombohedral region near the rhombohedral/tetragonal morphotropic phase boundary (MPB) is reported in this paper. A thermal-driven macrodomain– microdomain switching was revealed and confirmed for compositions close to the MPB in the rhombohedral region after poling. Morever, the transition from rhombohedral phase to tetragonal phase was first revealed in the curves of dielectric permittivity (or dissipation factor) versus temperature. This rhombohedral–tetragonal phase transition resulted from the MPB bending toward the rhombohedral phase region and was confirmed by high-temperature x-ray diffraction.

The structural deviation of boron-doped vapor-grown carbon fibers (VGCFs) with diameters around 10 μm relative to their undoped counterparts was investigated by polarized microprobe Raman spectroscopy and field-omission scanning electron microscopy as a function of heat-treatment temperature (HTT). Boron doping induces the formation of dislocation loops in the surface, which combine into larger loops with increasing HTT. The depolarization ratio, Dp, of the E2g2 mode for VGCFs increases gradually with increasing HTT, and finally approaches the value of highly oriented pyrolytic graphite, which is consistent with the asymmetric shape of the peak at ∼2725 cm−1 in the second-order Raman spectra. On the other hand, the Dp ratios of the E2g2 mode for boron-doped VGCFs show no deviations up to an HTT of 2100 °C, as compared to that of VGCFs, and decrease with increasing HTT, whereas the Dp ratios of the D peak show a maximum value at 2100 °C, and decrease gradually with increasing HTT. Consistent with these Raman results, boron atoms in the graphite lattice introduce a decreased d002 spacing (accelerating graphitization), but also hinder two-dimensional structural development and increase the amount of disorder. This is done by introducing tilt boundaries and vacancies, which make the Dp ratio of the E2g2 mode lower than the value for polycrystalline graphite, even though the fibers are heat treated at 2800 °C.

A new equation was developed for evaluating kinetic parameters in the isokinetic range of a phase transformation using nonisothermal calorimetric techniques. The Johnson–Mehl–Avrami equation was extended by considering that the transformation rate in an isothermal process can be translated into the nonisothermal transformation in an isokinetic range. The Avrami exponent, n, activation energy, E, and frequency factor, K0, were calculated from only one nonisothermal experiment by using the new kinetic equation for amorphous Se (a-Se), polysilane/polycarbosilane (PS/PCS), and lithium disilicate (LiO2 · 2SiO2 or LS2) samples with nucleation site saturation. The values of E and K0 calculated using the new kinetic equation agree well with those obtained by the Kissinger equation for the prenucleated a-Se, PS/PCS, and LS2 samples. The values of n indicate that volume crystallization is dominant in the bulk a-Se and LS2 samples, whereas surface crystallization is dominant in the powdered PS/PCS sample. These results for a-Se were confirmed by scanning and transmission electronic microscopy.

(Y + Sm)–α-sialon compositions with and without α-sialon seeds were hot-pressed at 1800 °C for 1 h and then heat treated at 1800 °C for 4 h. The effect of α-sialon seeds on the microstructures of (Y + Sm)–α-sialon ceramics was studied by scanning electron microscopy. The results showed that hot-pressed α-sialon ceramics with elongated grains can be fabricated by adding 10 wt% seeds. Through heat treatment, the seed-free composition could also develop into a similar microstructure with big elongated grains dispersed in a fine matrix.

The variation of the fracture toughness of MnZn ferrite ceramics with varying loading rate and humidity was determined with the aid of the single edge notched beam (SENB) test. A strong decrease with increasing humidity and decreasing loading rate was observed. A model for subcritical crack growth incorporating kinetic and adsorption effects was formulated to analyze the data. The value of the adsorptioncontrolled fracture toughness was determined independently by double torsion experiments and agreed favorably with the values as determined from the SENB data using the model. The strength of the material was determined, and analysis showed a strength behavior similar to the fracture toughness behavior, as predicted by the model. The analysis presented can be used to assess the subcritical crack growth behavior using a limited number of SENB specimens.

The structure-formation process and thermoelectric properties of binary and Fe-doped IrxSi1−x (0.30 ≤ x ≤ 0.41) thin films were investigated. The films were prepared by means of physical vapor deposition techniques, in particular by magnetron co-sputtering and electron beam co-evaporation. The amount of Fe dopant varied between 0 and 5 at.%. The phase-formation process depends on the volume fractions of the major components Ir and Si, whereas the small concentrations of dopant did not change the sequence of the crystalline phases formed. On the other hand, the thermoelectric transport properties correlate strongly with both the structure-formation process and the chemical composition of the films. Fe-doped iridium silicide films with useful thermoelectric power factors were successfully obtained by both magnetron co-sputtering and electron beam co-evaporation. A maximum thermoelectric power factor of 8.5 μW/(K2 cm) at 1200 K was observed for evaporated layers with thechemical composition Ir0.35Si0.63Fe0.02.

Si3N4 powders manufactured by two different preparative routes were characterized for the solid–liquid interfacial reactivity and surface composition. Three mixing processes were tried to investigate the modifications of silicon nitride particle surface in aqueous suspensions. The surfaces of the starting powders and the dried mixed powders were investigated by x-ray photoelectron spectroscopy to determine the nature and ratios of surface groups. Electroacoustic measurements show that no change occurs in the isoelectric point for the mixed Si3N4 powders while the milling/mixing process has a great influence on the zeta potential magnitude and particle size distribution.

The effect of ZrO2 addition on sintering behavior and mechanical properties of both hot-pressed and pressureless-sintered B4C was investigated. The addition of ZrO2 improved the densification behavior of B4C remarkably via a reaction with the B4C to form ZrB2 at elevated temperatures. When B4C was densified at 2000 °C by hot pressing, only a small amount (approximately 2.5 vol%) of ZrO2 was necessary to achieve a full densification. Excellent mechanical properties (hardness, elastic modulus, flexural strength, and fracture toughness) were observed in those specimens. As the amount of ZrO2 was increased further, the mechanical properties were reduced, except for the fracture toughness, apparently due to the formation of too much ZrB2 in the specimen. Without the applied pressure, larger amounts of ZrO2 should be added to obtain a body with high relative density. When the B4C was sintered at 2175 °C with addition of 10 vol% ZrO2, the specimen has a density higher than 95% of the theoretical, and hardness and flexural strength of 25 GPa and 400 MPa, respectively.

The ion damage produced in alloys of AlxGa1−xAs (x = 0.6, 0.7, 0.8, and 0.85) by implantation at 77 K with Kr ions (500, 700, and 1500 keV) was studied by using Rutherford backscattering channeling and transmission electron microscopy. In addition, the accumulation of ion damage at 50 K was studied by performing the ion implantations in situ in the transmission electron microscope. In Al0.8Ga0.2As, damage accumulation at 77 K was independent of dose rate, indicating that dynamic annealing is not occurring at 77 K. The in situ studies demonstrated that planar defects are produced on warm-up from 50 K to room temperature, indicating that they are not the nucleation site for amorphization. The lower energy implantations revealed that amorphization initiated within the AlxGa1−xAs layer, showing that heterointerfaces are not required for amorphization. These results, along with the similarity of the room-temperature microstructures in the different alloys, imply that the amorphization mechanism is independent of Al content. It is proposed that the observed dependence of the amorphization dose on Al content is related to an increase in the number of cascade overlaps needed to initiate and to produce a continuous amorphous layer. A mechanism explaining the microstructural changes with composition, based on the thermal and physical properties of the alloy and on the distribution of energetic cascade events, is presented.

A combined investigation of stress relaxation in WOxNy thin films sputter deposited on silicon wafers in an Ar–N2–O2 gas mixture by in situ substrate curvature measurements and of structural properties by ex situ x-ray diffraction, x-ray photoelectron spectroscopy, transmission electron microscopy (TEM), electron energy loss spectroscopy, and transmission electron diffraction is reported. It was found that the W2N films deposited under oxygen-free conditions had a high compressive stress of 1.45 GPa. As the oxygen concentration was increased, the stress became smaller and reached almost zero for films near 10–15 at.% oxygen. These results can be understood in terms of the decrease in the lattice parameter caused by substituting nitrogen atoms with oxygen in the lattice sites and the development of an amorphous network in the WOxNy films as the incorporation of oxygen was increased. Plan view and cross-sectional TEM analyses showed that 150-nm-thick oxygen-free crystalline W2N films had a columnar microstructure with an average column width of 15–20 nm near the film surface, whereas oxygen imbedded in the films provided a finer grain structure. The effect of oxygen in stabilizing the W2N structure was also elucidated and explained on the basis of structural and thermodynamic stability.

Epitaxial LiMn2O4 was successfully synthesized by coating a [Li–Mn–O] metalorganic precursor solution onto MgO (110) substrates at temperatures as low as 350 °C. Cross-sectional transmission electron microscopy observation revealed that the orientation relationship between LiMn2O4 and MgO was (111) LiMn2O4 //(111) MgO, (110) LiMn2O4 //(110) MgO, and [112] LiMn2O4 //[112] MgO, which resulted in the (111) LiMn2O4 planes growing perpendicular to the surface plane of MgO. The interface structure consisted of (111) layers of Mn atoms in the LiMn2O4 crystal aligned with the Mg atoms in the (111) planes of the MgO substrate when viewed along the [112] direction.

We fabricated Bi nanowire array composites with wire diameters from 30 to 200 nm by high-pressure injection (HPI) of Bi melt into porous anodic alumina templates. The composites were dense, with Bi volume fraction in excess of 50%. The parallel Bi nanowires, whose length appeared to be limited only by the thickness of the host template (up to 55 μm), terminated at both sides of the composite in the Bi bulk. The individual Bi nanowire crystal structure was rhombohedral, with the same lattice parameters as that of bulk Bi; the wires in the array were predominantly oriented with the trigonal axis along the wire length. Low contact resistance was achieved by bonding the composite to copper electrodes.

A model that finds the maximum permissible heating rate for pyrolysis of ceramic moldings is extended to produce multi-segment temperature–time profiles to minimize the binder removal time. The degradation of the polymer and the diffusion of degradation products in solution to the free surface in a cylinder containing 50 vol% alumina and polyalphamethylstyrene is considered. The theory has previously been validated experimentally for fixed heating rates for cylindrical and flat plate geometries and for overpressure debinding. The extended model, presented here, calculates the vapor pressure of monomer over solution and modifies the heating rate to keep this just below ambient pressure. In this way, the temperature follows the maximum allowable rate at each stage to prevent boiling and hence the incidence of defects.

Orientation-controlled epitaxial thin films of bismuth layer-structured ferroelectrics, SrBi2Ta2O9 (SBT) and SrBi2Nb2O9 (SBN), were prepared on single-crystal SrTiO3 (STO) substrates by the coating-pyrolysis process. Most of the SBT (SBN) films showed the (106) and (001) orientations on STO(110) and (001), respectively. The degree of orientation, in terms of the ratio of peak intensity to the background level in the x-ray diffraction φ-scan profile for the film, greatly increased with a decrease in the oxygen partial pressure, p(O2), of annealing atmosphere at 800 °C. Interestingly, coexistence of the (110)-oriented grains with the (106)-oriented ones on STO(110) [and the (100)-oriented grains with the (001)-oriented ones on STO(001)] was observed exclusively in the SBT films annealed at 700–750 °C under p(O2) of 10 Pa. Atomic force microscopy observations showed that the surface morphology of the SBT films remained almost unchanged, i.e., comprising round-shaped grains of submicrometer size, whereas that of the SBN films drastically changed, according to the variation in orientation of substrate surfaces or in annealing conditions, i.e., temperature, p(O2), and time.

The reaction of the bulk glass forming alloy Zr41Ti14Cu12Ni10Be23 (Vit 1) with W, Ta, Mo, AlN, Al2O3, Si, graphite, and amorphous carbon was investigated. Vit 1 samples were melted and subsequently solidified after different processing times on discs of the different materials. Sessile drop examinations of the macroscopic wetting of Vit 1 on the discs as a function of temperature were carried out in situ with a digital optical camera. The reactions at the interfaces between the Vit 1 sample and the different disc materials were investigated with an electron microprobe. The structure and thermal stability of the processed Vit 1 samples were examined by x-ray diffraction and differential scanning calorimetry. The results are discussed in terms of possible applications for composite materials.

Three mixing processes were used to introduce lanthanum oxide and yttrium oxide in silicon nitride suspensions. X-ray photoelectron spectroscopy (XPS) analysis was used to identify the surface composition and investigate the surface coverage by the added oxides. XPS results evidenced the protective effect against hydrolysis and oxidation of the coated layer. Electroacoustic measurements showed that the milling/mixing process and solids loading contents had a great influence on the isoelectric point (IEP) and on the dispersing degree for suspensions with sintering aids. With the change of solids load content and mixing energy, the IEP of mixed powders suspensions reflected a surface behavior dominated by the additives oxides. The attrition mixing and the ultrasonication resulted in the more efficient processing routes to distribute the sintering aids on the starting Si3N4 powders, especially at high solids volume fraction.

SiC, carbon, and Kevlart® fibers were coated with carboxylate–alumoxane nanoparticles and their calcium-, lanthanum-, and yttrium-doped analogs; firing to 1400 °C formed uniform aluminate coatings. Optimum processing sequences were determined. Both carboxylate–alumoxane- and ceramic-coated fibers were examined by field emission scanning electron microscopy, microprobe analysis, and optical microscopy. Coatings produced were stable to thermal cycling under air at 1400 °C. Fiber-reinforced ceramic matrix composites were prepared and results from 3-point bend tests for carbon/Kevlar®-fabric-reinforced ceramic matrix composites (CMCs) and carbon-fiber-reinforced CMCs were determined. Flexure strength for carbon-fiber- and carbon/Kevlart®-fiber-reinforced alumina CMCs was determined.